BoilerFaultCodesYour boiler has stopped working because it cannot safely clear away exhaust fumes or the internal fan has failed to start.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Fault on Fan or Flue
What causes this fault?
This fault occurs when the boiler's safety system detects that the fan isn't spinning fast enough or that exhaust gases aren't being pushed out of the flue correctly. It is often caused by a mechanical failure in the fan motor, a blockage in the flue pipe, or debris trapped in the small tubes that monitor airflow.
This issue can become more frequent during periods of high winds, which can create back-pressure in the flue and interfere with the air pressure sensor's readings.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like 25 — no call-out fees, no surprises.
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Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
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